VIZARD II: A Reconfigurable Interactive Volume Rendering System

VIZARD II: A Reconfigurable Interactive Volume Rendering System M. Meißner†, U. Kanus, G. Wetekam, J. Hirche, A. Ehlert, W. Straßer, M. Doggett*, P. Forthmann‡, and R. Proksa‡ WSI / GRIS, Universität Tübingen ‡Philips Research, Hamburg †Viatronix *ATI

Overview • Motivation • Features • System • RPU • Results & Future Work • Acknowledgments WSI/GRIS, University of Tübingen

Motivation • Need for interactive frame rates, the highest possible image quality, interactive change of parameters, and different rendering modes. • Learn from PC graphics (& from keynote): • Software (CPU) scales only with Moore’s Law but hardware can additionally scale by implementing the full algorithm (pipeline) in hardware and possibly parallel pipelines (SIMD) WSI/GRIS, University of Tübingen

Motivation • However, hardware (ASIC) is expensive, pays out only for large quantities, and change/ adaption in design requires new fabrication. • Thus, combine the performance of special purpose hardware with (almost) the flexibility of a software solution using reconfigurablelogic (FPGA). • Board can be re-used for other applications, e.g. volume reconstruction (Philips) WSI/GRIS, University of Tübingen

Features • Rays are cast from viewplane: • Flexible sampling rate • Trilinear interpolation • Post-classification • Per sample Phong shading • High precision compositing • Acceleration Techniques: • Geometry based space leaping • Early ray termination WSI/GRIS, University of Tübingen

Features • Ensure high(est) image quality by: • unlimited ray-casting including parallel and perspective projections • complex gradient filters mandatory for correct GM ( gradient as per voxel property) Left: Original volume rendering Right: Central difference, GM (>1), result depends on object orientation due to non symmetric gradient filter WSI/GRIS, University of Tübingen

Features • Ensure high(est) image quality by: • full classification withmaterial properties on a per sample base • additional interval based classification mode (pre-integration) and accurate combination with Phong shading[Meissner et al. GI2002] WSI/GRIS, University of Tübingen

System • Memory interface: • Trilinear interpolation requires eight Voxels in parallel. Ideally, one would like to have eight memory devices • For more flexibility, use exchangeable DIMMs instead of single SDRAM devices • DIMM modules are large in physical size and come in 64 data bits, thus use four – eight would not fit anyway - and store two voxel values (32 bit each) in one entry. WSI/GRIS, University of Tübingen

Replication System • Cubic memory organization:Volume is partitioned in sub-cubes and stored in linear memory (4 DIMMs, 64 bit) DIMM0 DIMM1 DIMM2 DIMM3 • 32x32x32 Voxel fit into Caches of 4 DIMMs --> ideal access time (e.g. 10ns) WSI/GRIS, University of Tübingen

System • Non blocking access using prefetching:Delay of page x-ings can be overlapped in time. [Doggett et al. HWW1999] No Time Yes WSI/GRIS, University of Tübingen

Ray Setup Ray casting SRAM SDRAM Xilinx Virtex DIMM DSP PCI Interface System bus PCI bus System PCI card (long!) Host computer WSI/GRIS, University of Tübingen

System DIMMs Power supplyand converters SRAM Reconfigurable chip (FPGA) DSP PCI interface chip WSI/GRIS, University of Tübingen

DIMMs SRAMs Sample props / pre-integration High frequency is challenging bandwidth is critical RC AU CU BU Combine TIU SU RPU • Central unit of VIZARD II is the RPU: RPU WSI/GRIS, University of Tübingen

RPU: Compositing • Compositing @ 100 MHz is a challenge: • Opacity: Ai+1 = Ai+ (1-Ai) * As • Inverse, multiply and subsequent Add of two 16 bit values is not feasible in 10ns • Use Threading: One compositing unit, multiple processed rays[Hesser VG ’99] WSI/GRIS, University of Tübingen

RC BU RPU: Compositing • Iteratively process n rays instead of one: • >= Eight rays allow frequency of 100 MHz + Better memory efficiency (overall less page x-ings) + Higher efficiency of early ray termination(overall pipeline latency is “divided” by number of rays)  Use early ray group termination WSI/GRIS, University of Tübingen

Results • Physical Design (~2 million gates) CU & SU BU Memory-Controller(s) DSP-I/O RC & AU TIU WSI/GRIS, University of Tübingen

Results WSI/GRIS, University of Tübingen

Results • DEMO WSI/GRIS, University of Tübingen

Results • VIZARDII VolumePro TexMap • Pipelines,@MHz 1@50 4@250 4@300 • Speed 3-7 >= 30 <=10 • Perspective yes (no) (yes) • Precision 16 12 8-10 • iso-surface yes no (yes) • Pre-integrated yes no (yes) • ERT & Co yes yes (no) WSI/GRIS, University of Tübingen

Results • Flexibility: Dual use of the same board!!! • Philips Research developed a design for volume reconstruction from projected images (C-arm CT, currently at 50 MHz) • 1. Reconstruction in 1 min (SW > 30 min) • 2. Subsequently interactive volume rendering of reconstructed data WSI/GRIS, University of Tübingen

Future Work • On-chip ray setup: Remove current bottleneck of system • Space Leaping: “Content based” real-time check of contributing 163 subcubes (50x per second) [Meissner et al. VG2001] • Non-photorealistic rendering: Technical drawings WSI/GRIS, University of Tübingen

Acknowledgements • Work: • Fellows and many many students • Funding: • German Research Council (DFG), grant 382 WSI/GRIS, University of Tübingen

Conclusion • Graphics Hardware WSI/GRIS, University of Tübingen

VIZARD II: A Reconfigurable Interactive Volume Rendering System